Copper complexes of the functionalised tripodal ligand tris(2-pyridyl)-methylamine and its derivatives

Article abstract of DOI:10.1039/b008476j

The coordination chemistry of the new tripodal ligand tris(2-pyridyl)methylamine (tpm) with copper(I), copper(II) and zinc(II) has been investigated. The synthesis of tpm can readily be modified to access a variety of related tripodal ligands such as 2-(methylsulfanyl)-1,1-di(2-pyridyl)ethylamine (mde); in addition, the primary amine function can be derivatised to extend further the range of complexes obtained, tpm itself is a versatile ligand, showing three distinct coordination modes: bidentate (py, NH₂), tridentate (2py, NH₂) and tridentate (3py). Complexes of stoichiometries Cu(tpm)_n (n = 1-3) have been obtained. The (2py, NH₂) coordination mode is illustrated by the crystal structure of [Cu(tpm)₂][BF₄]₂·Me₂CO, whilst (3py) coordination is found in the crystal structures of [Cu(SO₄)(tpm)-(H₂O)]·3H₂O, [{Cu(tpm)}₂Br₃]Br·3MeOH and also the zinc complex [Zn(tpm)(H₂O)₃]₂[Zn(H₂O)₆ ][SO₄]₃·3H₂O. Amide derivatives of tpm give complexes of stoichiometry CuL₂, and the crystal structures of [Cu(tpma)₂][BF₄]₂ [tpma = tris(2-pyridyl)methylacetamide] and [Cu(tpms)₂]·8H₂O {tpmsH = 4-oxo-4-[tris(2-pyridyl)methylamino]-butanoic acid} have been determined. The crystal structure of the sulfate-bridged dimeric complex [{Cu(SO₄)-(mde)}₂]·3H₂O shows the mde ligand to be tridentate, with (2py, NH₂) coordination.

Full text of DOI:10.1039/b008476j

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Copper complexes of the functionalised tripodal ligand tris(2-pyridyl)-
methylamine and its derivatives†
Phillip J. Arnold,a Sian C. Davies,b Jonathan R. Dilworth,c Marcus C. Durrant,*b
D. Vaughan Griffiths,a David L. Hughes,b Raymond L. Richardsd and Philip C. Sharpea
a Department of Chemistry, Queen Mary and Westfield College, Mile End Road, London,
UK E1 4NS
b Department of Biological Chemistry, John Innes Centre, Colney Lane, Norwich,
UK NR4 7UH
c Inorganic Chemistry Laboratory, South Parks Road, Oxford, UK OX1 3QR
d School of Chemistry, Physics and Environmental Science, University of Sussex, Brighton,
UK BN1 9QJ
Received 20th October 2000, Accepted 18th January 2001
First published as an Advance Article on the web 13th February 2001
The coordination chemistry of the new tripodal ligand tris(2-pyridyl)methylamine (tpm) with copper(), copper()
and zinc() has been investigated. The synthesis of tpm can readily be modified to access a variety of related tripodal
ligands such as 2-(methylsulfanyl)-1,1-di(2-pyridyl)ethylamine (mde); in addition, the primary amine function can be
derivatised to extend further the range of complexes obtained. tpm itself is a versatile ligand, showing three distinct
coordination modes: bidentate (py, NH2), tridentate (2py, NH2) and tridentate (3py). Complexes of stoichiometries
Cu(tpm)n (n = 1–3) have been obtained. The (2py, NH2) coordination mode is illustrated by the crystal structure
of [Cu(tpm)2][BF4]2ؒMe2CO, whilst (3py) coordination is found in the crystal structures of [Cu(SO4)(tpm)-
(H2O)]ؒ3H2O, [{Cu(tpm)}2Br3]Brؒ3MeOH and also the zinc complex [Zn(tpm)(H2O)3]2[Zn(H2O)6][SO4]3ؒ3H2O.
Amide derivatives of tpm give complexes of stoichiometry CuL2, and the crystal structures of [Cu(tpma)2][BF4]2
[tpma = tris(2-pyridyl)methylacetamide] and [Cu(tpms)2]ؒ8H2O {tpmsH = 4-oxo-4-[tris(2-pyridyl)methylamino]-
butanoic acid} have been determined. The crystal structure of the sulfate-bridged dimeric complex [{Cu(SO4)-
(mde)}2]ؒ3H2O shows the mde ligand to be tridentate, with (2py, NH2) coordination.
Our interests in this area stem from the identification by
Introduction
protein X-ray crystallography of the active site of copper-based
Tripodal ligands based on nitrogen heterocycles have secured
nitrite reductase (NiR) as a so-called ‘Type 2’ copper site.6–8 The
an important place in inorganic chemistry. The most extensive
contributions to date have been made in the field of poly-
coordination environment of Type 2 sites is provided by three
histidine ligands from the protein plus one or more exogenous
ligands. Similar sites are found in a wide variety of other
pyrazolylborate coordination compounds, first prepared by
Trofimenko in the 1960s.1 In the last few years, however, other
metalloenzymes containing copper and/or zinc, in addition
types of tripodal nitrogen ligand have received increasing
to NiR.7,9 Type 2 copper centres are generally involved in
attention, and the coordination chemistry of both tris-
catalysis and redox chemistry and typically have four- or
(pyrazolyl)methane2 and tris(2-pyridyl)3 ligands has recently
five-coordinate copper in geometries ranging from tetrahedral,
been reviewed. It has been suggested that pyridine is both a
as in NiR,6 to square pyramidal or trigonal bipyramidal.10 The
better σ donor and a better π acid than pyrazole,3 differences
Type 2 copper in NiR is situated in a hydrophobic pocket, some
12 Å from the protein surface. In addition, the enzyme contains
which should be reflected in the coordination chemistry of these
various classes of ligand. The tris(2-pyridyl) ligands (2-NC5-
a ‘Type 1’ copper centre which mediates electron transfer to
H4)3X reported to date encompass a very diverse selection of
the active site.8 The two copper centres are ca. 12.6 Å apart
bridgehead groups X, including CH, COH, N, P, PO, As, SnnBu
and linked directly through sequential histidine and cysteine
residues. Derivatisable tripodal ligands offer the opportunity
not only to model the immediate coordination environment of
the Type 2 copper, but also to build in other features of the
and Pb.3 Some of these ligands allow the possibility of elabor-
ation of their coordination chemistry via derivatisation of the
bridgehead group. For example, Levacher et al.4 linked the
carbinol (2-NC5H4)3COH to a polymeric support by derivatis-
protein environment such as hydrophobicity or connections to a
ation of the alcohol function to an ether; subsequent incorpor-
secondary metal centre. The theme of copper centres connected
ation of iron gave a material which proved to be an efficient
catalyst for methanolysis of styrene oxide. Recently, Jonas and
Stack have commented on the versatility of this type of ligand
and reported a systematic study of the copper coordination
by nitrogen donor ligands has also been explored in the wider
context of extended structural networks by the recent studies of
Blake et al.11
We have focussed our efforts on the new ligand tris(2-pyridyl)-
chemistry of the ligands (2-NC5H4)n[2-(6-MeO)C5H3N](3Ϫn)
-
methylamine, tpm, and related species, and a preliminary
account of our work has appeared.12 The synthesis of tpm is
readily modified to give a wide variety of related ligands, whilst
the primary amine function is well suited for derivatisation and
linking to other metal centres or solid supports. In this paper we
set out the coordination chemistry of tpm and related species
COMe (LOMe, n = 0 to 3).5
† Electronic supplementary information (ESI) available: preparation
and characterisation of amine derivative proligands. See http://
www.rsc.org/suppdata/dt/b0/b008476j/
736
J. Chem. Soc., Dalton Trans., 2001, 736–746
This journal is © The Royal Society of Chemistry 2001
DOI: 10.1039/b008476j

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and their amine derivatives with copper. The crystal structures
of six of the copper complexes and also a zinc complex of tpm
are reported.
complex molecule are part of one hydrogen-bonded layer, and
the tpm amine group links into the next layer. Within each layer
there are alternative networks involving either the major
components of the disordered sulfate and solvent molecules, or
the minor components; a view of the major system is shown in
Fig. 1(b).
Results and discussion
It is likely that the complexes [Cu(SO4)(L)(H2O)]ؒnH2O
(L = bpm, 2, L = bpqa, 3) are structurally analogous to 1. The
tpm ligand in the bromide complex [CuBr2(tpm)] 4 probably
also shares this coordination mode; 4 would then be analogous
to the structurally characterised [CuBr2(Mepy3CH)] (Mepy3-
CH = tris(6-methyl-2-pyridyl)methane).14 Upon recrystallis-
ation, complex 4 was converted into the bromide-bridged
dimeric cation [{Cu(tpm)}2Br3]ϩ 5. Although the crystal struc-
ture of 5 showed significant disorder in the anion and solvent of
crystallisation, the cation was well resolved (Fig. 2). One copper
atom, Cu(2), is octahedrally coordinated by the three tpm
pyridyl N atoms and three bromide ligands. The other is
The ligands used in this study are shown with their abbrevi-
ations in Scheme 1, and the physical and spectroscopic
five-coordinate with
a square pyramidal geometry; the
Cu(1) ؒ ؒ ؒ Br(1) distance is 2.980(4) Å, too long to be considered
a bond. It appears, then, that the three fac bromide ligands
cannot form triply bridging links between two copper atoms; as
it is, there is a wide range of Cu–Br bonding distances, from
2.492(3) to 2.737(2) Å, in this complex. Difference peaks in this
region suggest that in some cases the non-bridging bromide is
replaced by a bridging methoxide ion with more equal bonding
distances to the two copper atoms. The Cu2(µ-X)2 structural
motif is well established, but triple halide bridges to copper()
are much rarer, and appear to be confined to date to catenated
[{CuX3}n]nϪ species.15 In the case of [CuBr2(Mepy3CH)] the
methyl groups probably provide sufficient steric hindrance to
prevent formation of a dimer. In the structure of crystals of 5
the dimeric cation [{Cu(tpm)}2Br3]ϩ lies on a mirror plane of
symmetry and is elongated along the c axis, with the amine
groups directed towards the mirror planes at z = 1/4 and 3/4.
These planes, we believe, comprise networks of the anions and
solvent molecules, linked to each other and to the amine groups
by hydrogen bonds; the amine groups are hydrogen bonded to
two of the three acceptor groups arranged in an almost equi-
lateral triangle in the mirror plane. Each acceptor group com-
prises either a bromide ion (ca. 1/3 occupancy) or a solvent
molecule (MeOH or H2O, ca. 2/3 occupancy); the acceptor O
atom of the solvent molecule was located in each case about
0.5 Å closer to the BrϪ ion than to the amine N atom, but the
associated methyl group was not resolved, perhaps disordered
over several sites, hidden under the bromide peak or not present
(i.e. the solvent is a water molecule). A separate group of three
solvent atoms, each refined as a carbon atom, is probably a
solvent (MeOH) molecule disordered over the three sites, in
either direction, depending on the hydrogen bonds formed with
neighbouring groups.
The second coordination mode of tpm is illustrated by the
crystal structure of [Cu(tpm)2][BF4]2 6 (Fig. 3). Here the tpm
ligands are also tridentate and tripodally coordinated, but the
donor set comprises two pyridines and the primary amine. The
amine hydrogen atoms in the tpm ligands of this complex were
included in idealised positions and then allowed to refine freely.
Both are involved in N–H ؒ ؒ ؒ F hydrogen bonds to the dis-
ordered BF4Ϫ anions in either of two distinct orientations. The
copper complex cations and the anions are thus linked in
planar, hydrogen-bonded networks.
For both the (2py, NH2) and (3py) tridentate coordination
modes of tpm the three nitrogen atoms should form an equi-
lateral triangle in ideal tripodal symmetry. Although all of the
structurally characterised complexes in this study show some
distortion from this ideal symmetry, the distortion is signifi-
cantly increased for 6; the three nitrogen donors form an
approximate isosceles triangle with the largest angle (73.3Њ) sub-
tended at the amine. This increased distortion is probably
related to the fact that the bis(pyridine) amine coordination
Scheme 1
properties of their complexes are given in Table 1 and the
Experimental section. Most of the complexes contain solvent
of crystallisation, sometimes in variable proportions depending
on the procedure used to isolate the complex; this resulted in
some differences between the solvent stoichiometries given in
Table 1 and those determined by X-ray crystallography. The
parent ligand, tris(2-pyridyl)methylamine, tpm, is readily pre-
pared in 60% yield via a ‘one pot’ synthesis from 2-amino-
methylpyridine and 2-chloropyridine. Variation of the reaction
conditions allows isolation of the intermediate bis(2-pyridyl)-
methylamine, previously prepared by reduction of the corre-
sponding ketoxime,13 from which a variety of other potential
tripodal ligands are accessible. In all these compounds the
primary amine group is readily converted into amide or Schiff
base derivatives, which may themselves contain additional
functional groups.
tpm itself exhibits three different coordination modes, two of
which we have established by X-ray crystallography. The first is
illustrated by the sulfato complex [Cu(SO4)(tpm)(H2O)]ؒ3H2O 1
(Fig. 1), in which tpm is tridentate and coordinated through
the three pyridine nitrogen atoms. Complex 1 has a distorted
square pyramidal geometry, with a non-coordinated water
occupying the sixth coordination site in octahedral geometry.
Dimensions about the metal atom in this and the other com-
plexes described below are listed in Table 2. In these crystals the
Cu–tpm units bridge layers of hydrogen-bonded networks. The
coordinated water molecule, O(5), and the sulfate ligand of the
J. Chem. Soc., Dalton Trans., 2001, 736–746
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Table 1 Colours, conductivities and analyticala data for the copper complexes
Analysis (%)
C
Complex
Colour
ΛMb/S cm2 molϪ1
H
N
1 [Cu(SO4)(tpm)(H2O)]ؒ2H2O
2 [Cu(SO4)(bpm)(H2O)]ؒ2H2O
3 [Cu(SO4)(bpqa)(H2O)]ؒ4H2O
4 [CuBr2(tpm)]ؒ0.5H2O
Blue
15 (MeCN ϩ 20% water)
16 (MeOH)
2 (DMF)
40.1
(40.4)
41.7
(41.7)
43.7
(43.7)
38.9
(38.8)
37.0
(37.5)
51.4
(51.3)
56.0
(56.3)
50.3
(50.6)
50.8
(51.1)
55.7
(56.0)
54.7
(54.8)
59.3
(59.7)
53.1
(53.3)
46.0
(46.0)
49.9
(50.2)
52.1
(52.6)
40.2
4.2
(4.2)
4.4
(4.5)
4.3
(4.7)
2.8
(3.1)
3.2
(3.3)
4.3
(4.2)
4.1
(4.1)
4.3
(4.4)
3.8
(3.8)
5.2
(4.9)
3.8
(4.0)
6.5
(6.4)
6.0
(6.2)
4.1
(4.2)
4.3
(4.3)
4.4
(4.4)
3.6
11.6
(11.8)
11.3
(11.4)
9.1
Dark green
Turquoise
Green
(9.3)
11.1
(11.3)
10.9
(10.9)
13.7
(13.7)
16.4
(16.4)
11.8
(11.5)
13.1
(13.2)
13.0
(13.1)
11.1
(11.1)
9.9
(9.9)
8.7
(8.9)
8.4
(8.4)
9.8
(9.6)
11.4
(11.2)
10.3
(10.5)
9.5
(9.9)
9.7
(9.7)
13.1
(13.1)
36 (DMF)
5 [Cu2Br3(tpm)2]Brؒ3H2O
6 [Cu(tpm)2][BF4]2ؒC3H6O
7 [Cu(tpm)3][BF4]2
Brown
Blue
87 (DMF)
244 (MeCN)
308 (MeCN)
56 (MeOH)
292 (MeCN)
13 (MeOH)
13 (DMF)c
254 (MeCN)
0 (MeCN)
Green
8 [Cu(OAc)2(tpm)]ؒ0.5CH2Cl2
9 [Cu(tpma)2][BF4]2
Green
Lilac
10 [Cu(tpms)2]ؒ4H2O
Purple
11 [Cu(tpmb)2]ؒ3H2O
Lilac
12 [Cu(tpml)2][BF4]2
Purple
13 [Cu(SO4)(tpml)(H2O)]ؒ0.5H2O
14 [Cu3(OAc)4(mops)2(H2O)2]ؒCH2Cl2
15 [Cu(OAc)(bops)]ؒ0.5CH2Cl2
16 [Cu(OAc)(tpms)(H2O)]
17 [Cu4(SO4)4(bop)3]
Light blue
Turquoise
Blue
10 (MeCN ϩ 10% water)
13 (MeOH)
4 (DMF)
Light blue
Light blue
Blue
51 (MeOH)
5 (MeOH)
(40.4)
36.9
(36.9)
35.8
(36.1)
43.3
(43.3)
(3.4)
4.0
(4.1)
3.8
(4.2)
3.6
(3.8)
18 [{Cu(SO4)(mde)}2]ؒ2H2O
19 [Cu(SO4)(mde)(H2O)]ؒ0.5H2O
21 [Cu(tpm)(NCMe)]PF6ؒ0.33CH2Cl2
Green
15 (MeOH)
—
Pale green
a Calculated values in parentheses. b Accepted ranges24 for 1:1 and 1:2 electrolytes are as follows: DMF, 65–90 and 130–170 S cm2 molϪ1 respectively;
MeCN, 120–160 and 220–300 S cm2 molϪ1 respectively; MeOH, 80–115 and 160–220 S cm2 molϪ1 respectively. c Approximate value due to the
complex’s very poor solubility.
mode requires two 5- and one 6-membered chelate ring, where-
as in the tris(pyridine) mode all three chelate rings are
6-membered. As expected, complex 6 exhibits Jahn–Teller dis-
tortion, but with the elongated axial sites occupied by two of
the pyridines rather than the amine groups. This suggests that
stronger bonding between the copper and the amino group
compared to the pyridine nitrogens is offset by increased distor-
tion of the coordination sphere required to coordinate the
amine. Clearly, there is a fine balance between the tris-pyridine
and bis-pyridine/amine donor sets in these complexes. The
structure of complex 6 is closely related to that of [Cu-
(dipa)2][ClO4]2 [dipa = bis(2-pyridyl)methylamine];16 in this
case also, two of the pyridine groups occupy the elongated
axial positions. Interestingly, although [Cu(dipa)2]2ϩ and
[Cu(tpm)2]2ϩ show very similar equatorial Cu–N distances
(mean values 2.02 and 2.05 Å respectively), the axial Cu–N
distances show a much greater variation (2.54 and 2.36 Å
respectively). The relative weakness of these axial bonds prob-
ably makes them particularly susceptible to other influences,
in this case perhaps the increased steric requirements of the
bulkier tpm ligand compared to those of dipa.
of a new product, [Cu(tpm)3][BF4]2 7. Assuming octahedral
coordination, each of the ligands in this complex should be
bidentate, giving a third coordination mode for tpm. Molecular
models suggest that bidentate coordination can best be
achieved via one pyridine and the amine; coordination through
two pyridine rings is less likely not only on steric grounds,
but also by virtue of the chelate effect, since in this arrange-
ment the ligand is necessarily poised to become tridentate. It is
worth noting here that the analogous ligands LOMe (see above)
show bidentate coordination through two pyridines in the
structurally characterised copper() complexes [Cu(LOMe)2]-
[CF3SO3].5 However, the steric requirements of two LOMe
ligands in a tetrahedral arrangement should be significantly
lower than those of three tpm ligands in an octahedral
environment, as in complex 7. Attempts to recrystallise 7
returned complex 6.
Although use of Cu(BF4)2 as the copper starting material
tends to give complexes of 1:2 or 1:3 rather than 1:1 metal:
ligand stoichiometries, the converse is true for copper salts with
more strongly coordinating anions, such as CuSO4 and CuBr2,
as discussed above. Another example is provided by the acetato
complex [Cu(OAc)2(tpm)]ؒ0.5CH2Cl2 8, whose conductivity
(Table 1) suggests that both acetates remain coordinated in
solution. The best pointer to the structure of this complex
is probably the crystallographically characterised [Cu(OAc)2-
Since complex 6 was initially isolated from the reaction of
equimolar amounts of Cu(BF4)2 and tpm, we attempted a
rational preparation using a higher ratio of tpm. However, the
use of fairly concentrated reagent solutions led to precipitation
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J. Chem. Soc., Dalton Trans., 2001, 736–746

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Fig. 1 Crystal structure of [Cu(SO4)(tpm)(H2O)]ؒ3H2O 1. The complex molecule is shown in (a) and a layer of the hydrogen bonding network,
parallel to the a–b plane, in (b). In (b) the tpm ligand, which bridges the layers of hydrogen bond planes, is omitted for clarity. In all the molecular
diagrams the atom numbering schemes are indicated and hydrogen atoms are omitted for clarity.
Fig. 2 Crystal structure of the cation of [{Cu(tpm)}2Br3]Brؒ3MeOH
Fig. 4 Crystal structure of the cation of [Cu(tpma)2][BF4]2 9.
5.
Further control over the reaction products can be achieved
by restricting the available coordination modes of the tpm
ligand to the tris-pyridyl donor set, for example by derivatis-
ation of the primary amine function to an amide. Structurally
characterised examples of such complexes are provided by
[Cu(tpma)2][BF4]2 9 and [Cu(tpms)2]ؒ8H2O 10 (Figs. 4 and 5
respectively). The copper atoms in these homoleptic complexes
are in very similar Jahn–Teller distorted octahedral coordin-
ation environments. There is only one hydrogen atom available
for forming hydrogen bonds in 9, namely that of the amide
group. This hydrogen links to a fluorine atom of the BF4Ϫ anion
in either of its disordered orientations, thus forming discrete
hydrogen-bonded [Cu(tpma)2][BF4]2 units. Hydrogen atoms of
all the solvent water molecules in complex 10 were located in
difference maps and refined freely. These water molecules and
the carboxylate oxygen atoms of the tpms ligands are linked by
hydrogen bonds in layers, as shown in Fig. 5(b); the [Cu(tpms)2]
molecules lie between, and bridge, these layers.
Reaction of the ortho-sulfonic acid derivative tpmbH with a
variety of copper() starting materials produced in all cases the
homoleptic complex [Cu(tpmb)2] 11. The driving force for this
Fig. 3 Crystal structure of the cation of [Cu(tpm)2][BF4]2ؒMe2CO 6.
(py2NH)], py2NH = bis(2-pyridyl)amine,17 in which the py2NH
ligand coordinates through the two pyridine nitrogens, whilst
one acetato ligand is monodentate and the second is bidentate,
giving distorted square-pyramidal coordination overall. The
coordination sphere in complex 8 is probably similar, except
that the tpm ligand is most likely tridentate.
J. Chem. Soc., Dalton Trans., 2001, 736–746
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Fig. 5 Crystal structure of [Cu(tpms)2]ؒ8H2O 10. The complex molecule is shown in (a), and a layer of the hydrogen bonding network, viewed down
the (1 0 Ϫ1) axis, in (b). The copper and pyridine rings are omitted for clarity.
reaction is probably the very low solubility of 11 in all common
solvents, including DMF and water. The anomalous chemical
shifts of free tpmbH compared to the other tpm amides (see
Experimental section) suggest that this compound may exist as
its zwitterionic pyridinium sulfonate form in solution.
As an alternative to amide derivatisation, tpm can be con-
verted into a Schiff base such as tpmSB (Scheme 1). This
derivative proved less robust than the amides; thus, reaction of
tpmSB with copper() sulfate gave the tpm complex 1 plus free
benzaldehyde. However, we were able to prepare copper()
nitrite complexes of Schiff base ligands of this type.18
Derivatisation of the tpm ligand can be used to modify the
physical properties of the resulting complexes. Thus derivatis-
ation of tpm with lauroyl chloride leads to complexes with
significantly enhanced hydrophobicity, such as [Cu(tpml)2]-
[BF4]2 12 and [Cu(SO4)(tpml)(H2O)] 13, which are readily
soluble in solvents such as dichloromethane. Similarly, complex
9 is a 1:2 electrolyte whereas 10 is overall charge-neutral by
virtue of its pendant carboxylate groups. The carboxylate
groups in this kind of complex could in principle ligate a second
metal atom; this would account for the stoichiometry of the
trinuclear complex [Cu3(OAc)4(mops)2(H2O)2] 14, in which a
central Cu(mops)2 unit probably links two Cu(OAc)2 centres.
The central copper could possess an N6 coordination environ-
ment, similar to those of 9 and 10; however, comparison of the
colours of these complexes (Table 1) suggests that the structure
shown in Scheme 2 is more likely. The two terminal copper
atoms would then be structurally similar to those in complex
8. Hence, these functionalised ligands allow the possibility
of linking copper centres possessing different coordination
environments.
Scheme 2 Proposed structure of complex 14.
As well as derivatisation of tpm before metal complexation, it
proved possible to derivatise the amino group of coordinated
tpm, even when this group is itself initially coordinated. For
example, reaction of complex 6 with acetic anhydride gave the
corresponding tpma complex 9. The slow rate of this reaction
at room temperature, requiring days compared to hours for free
tpm, is presumably associated with the required change in the
coordination mode of the ligand.
In addition to derivatisation of the amine function of tpm,
substitution at the pyridine rings is also possible via modified
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J. Chem. Soc., Dalton Trans., 2001, 736–746

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Fig. 6 Crystal structure of the dimer complex in [{Cu(SO4)(mde)}2]ؒ
3H2O 18.
synthetic procedures. Such changes may give markedly different
copper complexes. Thus, whilst [Cu(OAc)(bops)] 15 appears to
be a direct analogue of [Cu(OAc)(tpms)(H2O)] 16, reaction of
bop with CuSO4 did not give an analogue of 1 but an appar-
ently polynuclear complex, [Cu4(SO4)4(bop)3] 17. The thioether
ligand mde (Scheme 1) gave two distinct complexes, both
formulated as Cu(SO4)(mde)(H2O)n, 18 and 19. It appears that
they do not interconvert in solution. Of the two, only 18 could
be crystallised; the crystal structure (Fig. 6) shows a dimeric
structure in which the mde ligands are tridentate, each coordin-
ated via the two pyridine rings and the amine nitrogen, analo-
gous to the second coordination mode of tpm discussed above.
The two Cu(mde) units are bridged about a centre of symmetry
by the two sulfate ligands. Of the two independent solvent
water molecule sites in [{Cu(SO4)(mde)}2]ؒ3H2O, 18, one
appears to be only half occupied. The hydrogen atoms of the
water molecule in the fully occupied site and of the amine
ligand were located and refined, and all form hydrogen bonds
so that the dimer molecules are linked in sheets through the
crystal. The sheets are linked only by rather weaker hydrogen
bonds through the partial-occupancy water molecules.
Comparison of all of the structurally characterised
copper() complexes obtained in this work reveals a common
distortion in which the plane of the coordinated pyridine ring
deviates from the ideal orientation parallel to the Cu–N bond
vector. This can be quantified by the angle formed between the
Cu–N bond and the N–C diagonal of the pyridine ring, ideal
value 180Њ. The greatest distortion is found in complex 6, where
one of these angles is 158.1(1)Њ. This phenomenon probably
originates in the Jahn–Teller effect, since it appears to be absent
in the zinc cations [Zn(tpm)(H2O)3]2ϩ 20 [Fig. 7; Zn–N–C
angles 172.1(2)–178.0(2)Њ]. There are two distinct [Zn(tpm)-
(H2O)3]2ϩ cations and one [Zn(H2O)6]2ϩ cation in the crystal,
and these are arranged in layers parallel to the a–b plane: layer
I, at z = 0, comprises cations of the first type, namely the cation
of Zn(1); layer II, about z = ½, is a very similar layer of the
second, Zn(2), cation. These cations are separated by layer III,
at z = ¼ and ¾, which comprises the Zn(3) [Zn(H2O)6]2ϩ
cations, the sulfate anions and the water molecules. Layer III is
an extensively hydrogen-bonded system linking all moieties and
involving, also, all the coordinated water molecules and the tpm
amine groups. Each cation in layers I and II bridges two layers
III, with its water ligands in one layer III and its amine
group in the next. The extensive hydrogen bonding might
account for the preservation of the stoichiometry of this com-
plex on recrystallisation.
Fig. 7 Crystal structure of one of the two virtually identical tpm-
containing cations of [Zn(tpm)(H2O)3]2[Zn(H2O)6][SO4]3ؒ3H2O 20.
tpm ligand. The crystal structures of analogous complexes
[Cu(LOMe)(NCMe)][CF3SO3] have recently been reported.5
Free tpm shows the characteristic pyridine π–π* absorption
at 263 nm in acetonitrile solution. This band is essentially
unchanged in position, but increased in intensity, in the spectra
of all the complexes (see Experimental section). The relatively
weak copper() d–d band ranges from 570 to 715 nm. The IR
spectra of tpm and its amide derivatives show weak bands at
3200–3400 cmϪ1 associated with ν(NH) (see Experimental
section). These bands are generally also present in the spectra
of the complexes, unless obscured by water of crystallisation.
The amide I band appears at 1630–1695 cmϪ1 for the free
amides and their complexes. Although the carbonyl group is
not involved in coordination, the band generally shows a
significant shift to higher wavenumbers in the spectra of the
complexes. The shift presumably has its origin in the overall
electronic state of the ligand, since it is larger for the anionic
ligand tpmsϪ (50–60 cmϪ1) than the neutral ligands tpma and
tpml (20–35 cmϪ1). tpmbH again provides the exception, with
the amide I band shifted to lower wavenumbers by 14 cmϪ1 for
complex 11 compared to the “free” ligand. This may be associ-
ated with an internal hydrogen bond between the amide
NH and the sulfonate group. The pyridine rings give medium
intensity bands at 1530–1600 cmϪ1, which generally show small
shifts (maximum 12 cmϪ1) to higher wavenumbers on coordin-
ation. Whereas [Cu(tpma)2][BF4]2 9 shows two such bands,
[Cu(tpm)2][BF4]2 6 gives three and [Cu(tpm)3][BF4]2 7 four, pre-
sumably a consequence of the presence of both coordinated
and non-coordinated pyridine rings in the last two complexes.
All of the ligands and their complexes show a variable number
of generally sharp, medium intensity bands below 1200 cmϪ1
,
highly characteristic of the individual compound but of
Ϫ
Ϫ
little diagnostic value. The SO42Ϫ, BF4 and PF6 anions give
characteristic strong IR features.
Conclusion
tpm and its substituted derivatives constitute a versatile new
class of tripodal ligands for copper and other metals. The syn-
thetic procedures described in this work can readily be extended
to give compounds incorporating one or more substituted
pyridines, or indeed completely different functional groups
such as thioethers. An entirely separate approach to derivatis-
ation is provided by the primary amine function. Conversion of
this group into an amide, Schiff base or other derivative can be
used to tune the properties of the resulting complexes such as
charge, solubility, etc. Such derivatisation may be carried out
before or after complexation to the metal. Incorporation of
further functional groups in this way can be used to link the
The diamagnetic copper() complex [Cu(tpm)(NCMe)]PF6
21 proved highly air-sensitive in solution, frustrating attempts
at crystallisation. This contrasts with the related tris-
(pyrazolylmethane) complexes [Cu(HC{3-Rpz})(NCMe)]PF6,
which are described as ‘moderately air-stable even as solu-
tions’,2 and is possibly due to the more open nature of
the copper site in 21. Based on the NMR data, complex 21 is
probably tetrahedral, with a tris-pyridyl donor set for the
J. Chem. Soc., Dalton Trans., 2001, 736–746
741

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Table 2 Bond lengths (Å) and angles (Њ) about the metal atoms in the copper and zinc complexes
[Cu(SO4)(tpm)(H2O)]ؒ3H2O 1 [{Cu(mde)(SO4)}2]ؒ3H2O 18 [{Cu(tpm)}2Br3]Brؒ3MeOH 5
Cu–N(11)
Cu–N(21)
Cu–N(31)
Cu–O(41)
Cu–O(5)
Cu–O(6)
2.192(5)
2.017(5)
2.019(5)
1.941(5)
2.018(6)
2.658(10)
Cu–N(11)
Cu–N(21)
Cu–N(3)
Cu–O(51)
Cu–O(52Ј)
2.336(4)
2.027(4)
1.980(4)
1.959(3)
1.940(3)
Cu(1)–N(11a)
Cu(1)–N(21a)
Cu(1) ؒ ؒ ؒ Br(1)
Cu(1)–Br(2)
Cu(1)–O(1x)
O(1x)–C(1x)
2.134(13)
2.060(10)
2.980(4)
2.508(2)
2.135(2)
1.57(4)
Cu(2)–N(11b)
Cu(2)–N(21b)
Cu(2)–Br(1)
Cu(2)–Br(2)
Cu(2)–O(1x)
2.034(13)
2.099(10)
2.492(3)
2.737(2)
2.199(2)
Angles subtended at Cu
N(21)/N(11)
N(31)/N(11)
O(41)/N(11)
O(5)/N(11)
N(21)/N(31)
O(41)/N(21)
N(21)/O(5)
O(41)/N(31)
O(5)/N(31)
O(41)/O(5)
87.4(2)
85.8(2)
92.3(2)
93.6(2)
85.6(2)
177.4(2)
91.3(2)
91.8(2)
176.9(2)
91.3(2)
N(11)/N(21)
N(11)/N(3)
N(11)/O(51)
N(11)/O(52Ј)
N(21)/N(3)
N(21)/O(51)
N(21)/O(52Ј)
N(3)/O(51)
N(3)/O(52Ј)
O(51)/O(52Ј)
85.9(2)
73.7(2)
108.68(14)
113.04(14)
80.2(2)
160.5(2)
94.2(2)
91.4(2)
N(11a)/N(21a)
Br(2)/N(11a)
N(21a)/N(21aЈ)
Br(2)/N(21a)
Br(2)/N(21aЈ)
Br(2)/Br(2Ј)
N(11a)/O(1x)
N(21a)/O(1x)
O(1x)/Br(2)
87.4(4)
97.0(3)
85.3(5)
N(11b)/N(21b)
Br(1)/N(11b)
Br(2)/N(11b)
N(21b)/N(21bЈ)
Br(1)/N(21b)
Br(2)/N(21b)
Br(2)/N(21bЈ)
Br(1)/Br(2)
Br(2)/Br(2Ј)
N(11b)/O(1x)
N(21b)/O(1x)
O(1x)/Br(2)
84.7(4)
177.8(4)
92.5(3)
88.2(5)
93.8(3)
93.2(3)
175.3(3)
87.94(10)
175.4(4)
96.0(3)
96.3(3)
174.4(3)
89.23(8)
78.99(9)
161.8(4)
108.1(3)
73.65(6)
171.1(2)
91.8(2)
79.74(7)
[Cu(tpm)2][BF4]3ؒMe2CO 6
[Cu(tpma)2][BF4]2 9
[Cu(tpms)2]ؒ8H2O 10
Cu–N(11)
Cu–N(21)
Cu–N(1)
2.360(3)
2.041(2)
2.063(2)
Cu–N(11)
Cu–N(21)
Cu–N(31)
2.027(4)
2.357(4)
2.003(4)
Cu–N(11)
Cu–N(21)
Cu–N(31)
2.006(2)
2.033(2)
2.342(2)
Angles subtended at Cu
N(11)/N(21)
N(11)/N(1)
N(21)/N(1)
88.95(8)
72.10(9)
77.26(9)
N(11)/N(21)
N(31)/N(11)
N(31)/N(21)
86.7(2)
86.1(2)
83.3(2)
N(11)/N(21)
N(11)/N(31)
N(21)/N(31)
85.81(7)
84.07(7)
87.37(7)
[Zn(tpm)(H2O)3]2[Zn(H2O)6][SO4]3ؒ3H2O 20
Zn(1)–N(11) 2.111(3)
Zn(1)–N(21) 2.131(3)
Zn(1)–N(31) 2.137(3)
Zn(1)–O(41) 2.094(4)
Zn(1)–O(42) 2.090(3)
Zn(1)–O(43) 2.112(4)
Zn(2)–N(51)
2.118(3)
2.135(3)
2.139(4)
2.099(3)
2.095(4)
2.094(4)
Zn(3)–O(81)
Zn(3)–O(82)
Zn(3)–O(83)
Zn(3)–O(84)
Zn(3)–O(85)
Zn(3)–O(86)
2.106(3)
2.140(3)
2.156(3)
2.063(3)
2.076(3)
2.060(3)
Zn(2)–N(61)
Zn(2)–N(71)
Zn(2)–O(44)
Zn(2)–O(45)
Zn(2)–O(46)
Angles subtended at the Zn atoms
N(11)/N(21)
N(11)/N(31)
O(41)/N(11)
O(42)/N(11)
N(11)/O(43)
N(21)/N(31)
O(41)/N(21)
O(42)/N(21)
O(43)/N(21)
O(41)/N(31)
O(42)/N(31)
O(43)/N(31)
O(42)/O(41)
O(41)/O(43)
O(42)/O(43)
86.02(13)
83.83(13)
176.1(2)
92.46(14)
91.3(2)
83.86(13)
93.5(2)
92.15(13)
177.28(14)
92.3(2)
174.72(14)
96.03(14)
91.4(2)
N(51)/N(61)
N(51)/N(71)
O(44)/N(51)
O(45)/N(51)
O(46)/N(51)
N(61)/N(71)
O(44)/N(61)
O(45)/N(61)
O(46)/N(61)
O(44)/N(71)
O(45)/N(71)
O(46)/N(71)
O(45)/O(44)
O(46)/O(44)
O(46)/O(45)
85.43(13)
85.05(13)
92.17(13)
92.59(14)
177.9(2)
83.37(13)
89.59(14)
177.7(2)
92.5(2)
172.61(14)
95.3(2)
94.3(2)
91.6(2)
88.3(2)
O(81)/O(82)
O(81)/O(83)
O(84)/O(81)
O(85)/O(81)
O(86)/O(81)
O(82)/O(83)
O(84)/O(82)
O(85)/O(82)
O(86)/O(82)
O(84)/O(83)
O(85)/O(83)
O(86)/O(83)
O(84)/O(85)
O(86)/O(84)
O(86)/O(85)
178.32(13)
93.70(14)
92.77(14)
85.91(14)
92.9(2)
87.97(13)
87.44(13)
92.44(12)
86.99(13)
87.41(14)
175.27(13)
89.82(14)
87.90(13)
173.86(14)
94.91(14)
89.2(2)
87.79(14)
89.4(2)
complexes to secondary metal centres, or to solid supports such
as polymers, in principle allowing coupling of a catalytic site to
an electron transfer centre.
under nitrogen. [Cu(NCMe)4]PF6 was prepared by the liter-
ature procedure.19 Infrared (400–4600 cmϪ1, Nujol mulls) and
UV-vis (200–800 nm) spectra were recorded using Shimadzu
FTIR-8300 and UV-2101PC spectrophotometers respectively.
1H, 13C and 31P NMR spectra were recorded at 270.17, 67.94
and 109.38 MHz respectively using a JEOL GSX270 spec-
trometer and chemical shifts are quoted relative to external
SiMe4 or P(OMe)3 (note superscripts used below in the 1H and
13C assignments refer to the heterocyclic rings). Melting points
and solution conductivities were obtained using an Electro-
thermal melting-point apparatus and a Portland Electronic
conductivity meter respectively. Microanalyses were determined
by Mr. A. Saunders (University of East Anglia). Electron
impact mass spectra were obtained at 8 keV on a Kratos
MS50TC instrument at Queen Mary and Westfield College,
FABS mass spectra by Dr M. Cocksedge at the ULIRS Mass
Spectrometry Facility, London. Details of the preparation and
The penalty for such flexibility in ligand design is the
unpredictability of the resulting coordination chemistry. The
variability of copper coordination chemistry is highlighted
both in the present study and in literature reports on related
systems. As well as the principles of ligand design emerging
from this and other studies, use of coordinating anions such as
sulfate can help to control complex formation. With respect to
copper-based nitrite reductase, our next report in this area will
deal with the preparation and characterisation of copper nitrite
complexes of these ligands.
Experimental
Copper() compounds were prepared under air, other species
742
J. Chem. Soc., Dalton Trans., 2001, 736–746

View Article Online
characterisation of the amine derivative proligands have been
deposited as ESI.
(C7Ј), 127.2 (C5Ј), 126.9 (C10Ј), 126.2 (C6Ј), 123.0 (C3), 121.9 (C3Ј),
121.7 (C5) and 70.7 (CNH2). IR: 3353w and 3283m (NH2),
3051w, 3001w, 2929w, 1578m and 1585m (py ring), 1501m,
1462m, 1431m, 1308m, 1123w, 995m, 957w, 887w, 837m, 778m
and 752m cmϪ1. The preparation of bpqa from bpq is given as
ESI.†
Preparations
Tris(2-pyridyl)methylamine,
tpm,
1,1-bis(6-methoxy-2-
pyridyl)-1-(2-pyridyl)methylamine, bop, and bis(2-pyridyl)-
methylamine. A solution of 2-aminomethylpyridine (10.8 g, 100
mmol) in dry THF (110 cm3) was cooled to Ϫ78 ЊC under N2
and n-butyllithium (40 cm3 of 2.5 M solution in hexane, 100
mmol) added dropwise. The mixture was allowed to rise slowly
to room temperature and stirred for 24 h. 2-Chloropyridine
(11.4 g, 100 mmol) was added dropwise and the mixture stirred
for 24 h. Water (30 cm3) was added and the mixture stirred for
30 min. The volatile components were removed in vacuo and the
residue was partitioned between CH2Cl2 and water. The layers
were separated and the aqueous layer was extracted with
CH2Cl2. The organic layers were combined, dried over MgSO4
and reduced in vacuo. The resulting oil was triturated with
Et2O–hexane (1:1) to give a solid, which was recrystallised
from near-boiling water as tpm (7.8 g, 60%). (Found: C, 73.1;
H, 5.3; N, 21.2. Calc. for C8H7N2: C, 73.3; H, 5.4; N, 21.4%).
mp 98 ЊC. 1H NMR (CD2Cl2): δ 8.53 (m, 3H, H6), 7.62 (m, 3H,
H4), 7.35 (m, 3H, H3), 7.17 (m, 3H, H5) and 3.34 (br s, 2H,
exchanges with D2O, NH2). 13C NMR (CD2Cl2): δ 165.6 (s, C2),
148.8 (d, JCH = 178, C6), 136.3 (d, JCH = 161, C4), 123.4 (d,
JCH = 168, C3), 122.1 (d, JCH = 164 Hz, C5) and 70.6 (s, CNH2).
IR: 3362w and 3294w (NH2), 1583m and 1568m (py ring),
A similar procedure, using chloromethyl methyl sulfide in
place of 2-chloroquinoline, gave after chromatography using
silica–ethyl acetate, mde in 67% yield (Found: [MϩH]ϩ, m/z
1
246.1080. Calc. for C13H16N3S: 246.1065). H NMR (CDCl3):
δ 8.53 (m, 2H, H6), 7.54–7.64 (m, 2H, H4), 7.49–7.53 (m, 2H,
H3), 7.05–7.15 (m, 2H, H5), 3.63 (s, 2H, CH2), 3.27 (br s, 2H,
NH2) and 1.89 (s, 3H, CH3). 13C-{1H} NMR (CDCl3): δ 163.6
(C2), 148.0 (C6), 136.0 (C4), 121.5 (C3), 121.2 (C5), 64.6 (CNH2),
47.3 (CH2) and 17.1 (CH3). IR: 3367w and 3296w (NH2),
3053m, 3003m, 2916, 1587m and 1568m (py ring), 1463m,
1429m, 1151w, 995m, 750m, 650m and 619m cmϪ1
.
(6-Methoxy-2-pyridyl)bis(2-pyridyl)methylamine, mop and
(6-methyl-2-pyridyl)bis(2-pyridyl)methylamine, bpm. A solution
of bis(2-pyridyl)methylamine (2.0 g, 10.8 mmol) in dry THF
(40 cm3) was cooled to Ϫ78 ЊC under N2 and n-butyllithium
(4.3 cm3, 2.5 M, 10.8 mmol) added dropwise. The mixture was
allowed to warm slowly to room temperature and stirred for
4 h. 2-Chloro-6-methoxypyridine (1.55 g, 10.8 mmol) was
added dropwise (with care) and the mixture heated under reflux
for 18 h. Once cool, water (15 cm3) was added and the mixture
reduced to dryness in vacuo. The residue was taken up in
CH2Cl2 and the solution was washed with water, dried over
MgSO4 and reduced in vacuo. The product was purified by
column chromatography on silica using ethyl acetate–MeOH
(200:3) as eluent to give a red oil characterised as mop
(2.6 g, 84%). (Found: Mϩ, m/z 292.1324. Calc. for C17H16N4O:
1148m, 993m, 876m, 772m, 746m, 660m, 619m and 586m cmϪ1
.
UV (MeCN): 263 nm (ε 9580 MϪ1 cmϪ1).
A similar procedure, using 2-chloro-6-methoxypyridine in
place of 2-chloropyridine, gave after recrystallisation from
Et2O–hexane, bop in 17% yield (Found: C, 67.2; H, 5.6; N,
17.2%; Mϩ, m/z 322.1432. Calc. for C9H9N2O: C, 67.1; H, 5.6;
N, 17.4%; m/z 322.1430). mp 75 ЊC. 1H NMR (CDCl3):
δ 8.56 (m, 1H, H6), 7.58 (m, 1H, H4), 7.50 (m, 2H, H4Ј), 7.30 (m,
1H, H3), 7.13 (m, 1H, H5), 6.91 (m, 2H, H3Ј), 6.60 (m, 2H, H5Ј),
3.74 (s, 6H, CH3) and 3.37 (br s, 2H, NH2). 13C-{1H} NMR
(CDCl3): δ 165.4 (C2), 162.9 (C6Ј), 161.1 (C2Ј), 148.4 (C6), 138.7
(C4Ј), 135.6 (C4), 123.4 (C5), 121.6 (C3), 115.8 (C5Ј), 108.8 (C3Ј),
69.9 (CNH2) and 53.0 (CH3). IR: 3364m and 3294m (NH2),
3067w, 2943m, 2905w, 2851w, 1574s and 1563m (py ring), 1466s,
1427s, 1312s, 1261s, 1211m, 1169m, 1150w, 1119w, 1072w,
1
292.1324). H NMR (CDCl3): δ 8.54 (m, 2H, H6), 7.55 (m,
2H, H4), 7.48 (m, 1H, H4Ј), 7.33 (m, 2H, H3), 7.10 (m, 2H,
H5), 6.91 (m, 1H, H3Ј), 6.58 (m, 1H, H5Ј), 3.71 (s, 3H, CH3)
and 3.41 (br s, 2H, NH2). 13C-{1H} NMR (CDCl3): δ 164.9
(C2), 162.6 (C6Ј), 161.7 (C2Ј), 148.3 (C6), 138.5 (C4Ј), 135.6
(C4), 122.9 (C5), 121.4 (C3), 115.4 (C5Ј), 108.6 (C3Ј), 69.8
(CNH2) and 52.7 (CH3). The preparation of mops from mop
is given as ESI.†
A similar procedure, using 2-chloro-6-methylpyridine in
place of 2-chloro-6-methoxypyridine, gave, after recrystallis-
ation of the crude product from Et2O–hexane, bpm in 61%
yield (Found: [M ϩ H]ϩ, m/z 277.1464. Calc. for C17H18N:
1030m, 988m, 907m, 849w, 799m, 764m, 698w and 602m cmϪ1
.
Use of the same quantities and procedure, except that the
2-chloropyridine was added over 20 min and the water quench
added after stirring for 20 min rather than 24 h, gave bis(2-
pyridyl)methylamine as a yellow oil (20.3 g, 43%). bp 85 ЊC at
0.03 Torr (lit.13 147–151 ЊC at 0.57 Torr). Spectroscopic proper-
ties as reported.13
1
277.1453). mp 54 ЊC. H NMR (CDCl3): δ 8.56 (m, 2H, H6),
7.61 (m, 2H, H4), 7.47 (m, 1H, H4Ј), 7.40 (m, 2H, H3), 7.13 (m,
2H, H5), 7.01 (m, 2H, H3Ј/5Ј), 2.86 (br s, 2H, NH2) and 2.49 (s,
3H, CH3). 13C-{1H} NMR (CDCl3): δ 165.5 (C2), 163.3 (C2Ј),
157.3 (C6Ј), 148.6 (C6), 136.0 (C4/4Ј), 123.0 (C3), 121.6 (C5), 121.3
(C3Ј), 120.2 (C5Ј), 70.1 (CNH2) and 24.5 (CH3). IR: 3368w and
3302w (NH2), 3051w, 2924w, 1686w, 1585m (py ring), 1508w,
Bis(2-pyridyl)-1-(2-quinolyl)methylamine, bpq, and 2-(methyl-
sulfanyl)-1,1-bis(2-pyridyl)ethylamine, mde. A solution of bis-
(2-pyridyl)methylamine (1.5 g, 8.1 mmol) in dry THF (30 cm3)
was cooled to Ϫ78 ЊC under N2 and n-butyllithium (4.8 cm3,
2.5 M, 8.1 mmol) added dropwise. The mixture was allowed
to warm slowly to room temperature and stirred for 2 h.
2-Chloroquinoline (1.3 g, 8.1 mmol) in dry THF (5 cm3) was
added dropwise (with care) and the mixture stirred for 24 h.
Water (20 cm3) was added and the layers were separated. The
aqueous layer was extracted with CH2Cl2. The organic layers
were combined, dried over MgSO4 and reduced in vacuo. The
residue was purified by column chromatography using silica
and ethyl acetate, then recrystallised from CH2Cl2 as bpq (1.2 g,
47%). (Found: Mϩ, m/z 312.1375. C20H16N4 requires 312.1375).
mp 82 ЊC. 1H NMR (CDCl3): δ 8.56 (m, 2H, H6), 8.03 (m, 2H,
H4Ј/8Ј), 7.64 (m, 2H, H4), 7.56 (m, 1H, H5Ј), 7.45 (m, 2H, H3),
7.43Ϫ7.67 (m, 3H, H3Ј/6Ј/7Ј), 7.13 (m, 2H, H5) and 3.51 (br s,
2H, NH2). 13C-{1H} NMR (CDCl3): δ 165.1 (C2), 164.4 (C2),
148.6 (C6), 146.9 (C9Ј), 136.1 (C4), 135.3 (C8Ј), 129.4 (C4Ј), 129.0
1458m, 1431m, 1319w, 1123w, 995m, 775w and 748m cmϪ1
.
[Cu(SO4)(tpm)(H2O)]ؒ2H2O 1, [Cu(SO4)(bpm)(H2O)]ؒ2H2O
2 and [Cu(SO4)(bpqa)(H2O)]ؒ4H2O 3. A solution of CuSO4ؒ
5H2O (0.47 g, 1.9 mmol) in water (5 cm3) was added to a solu-
tion of tpm (0.50 g, 1.9 mmol) in ethanol (10 cm3). The mixture
was kept until most of the solvent had evaporated; the resulting
crystalline precipitate was filtered off, washed with ethanol, and
dried in vacuo as [Cu(SO4)(tpm)(H2O)]ؒ2H2O 1 (0.65 g, 73%).
IR (KBr disc): 3341s, br (H2O), 1593m (py ring), 1467m,
1442m, 1116s, br (SO4), 1053m, 976m, 781m, 759m, 653m,
507w, 435w and 421w cmϪ1. UV–VIS (MeCN ϩ 10% water):
656 (71) and 263 nm (ε 12500 MϪ1 cmϪ1). Slow evaporation of
a methanol–water solution of complex 1 in an open tube gave
crystals suitable for X-ray diffraction.
A similar procedure using bpm rather than tpm gave, after
trituration of the precipitate with acetone, [Cu(SO4)(bpm)-
(H2O)]ؒ2H2O 2 in 84% yield. IR: ca. 3373m, br (H2O), 1591m
J. Chem. Soc., Dalton Trans., 2001, 736–746
743

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and 1570m (py ring), 1304w, 1113s, br (SO4), 1026s, 966m,
773m, 721m and 610m cmϪ1. UV–VIS (MeOH): 664 (79), 358sh
(1650) and 263 nm (ε 15000 MϪ1 cmϪ1).
Likewise use of bpqa gave [Cu(SO4)(bpqa)(H2O)]ؒ4H2O 3
in 23% yield. IR: ca. 3363m, br (H2O), 1680m (amide I),
1599m (py ring), 1279m, 1157m (SO4), 1109m, 1038m, 968m,
764m, 752m, 621m and 556w cmϪ1. UV–VIS (DMF): 628 nm
(ε 102 MϪ1 cmϪ1).
of [Cu2(OAc)4(H2O)2] (0.055 g, 0.14 mmol) in a little water was
added to a warm solution of tpmsH (0.20 g, 0.552 mmol) in 1:1
ethanol–water (20 cm3). The mixture was evaporated to small
volume in a nitrogen stream, then filtered, and the solid was
dissolved in water. The solution was filtered, and acetone added
to the filtrate until the first permanent precipitate was observed.
The mixture was kept overnight, and the precipitate was filtered
off as [Cu(tpms)2]ؒ4H2O 10 (0.11 g, 47%). IR: 3352m, 3271m,
1686m (amide I), 1597m (py ring), 1564m (CO2), 1202w, 1161w,
1028w, 1007w, 777m, 721w and 573w cmϪ1. UV–VIS (MeOH):
587 (30) and 260 nm (ε 24400 MϪ1 cmϪ1). X-Ray quality crystals
were obtained overnight by careful dilution of an aqueous
solution of complex 10 with acetone until the first permanent
precipitate was observed.
[CuBr2(tpm)]ؒ0.5H2O 4 and [Cu2Br3(tpm)2]Br 5. A solution
of tpm (0.24 g, 0.92 mmol) and CuBr2 (0.20 g, 0.90 mmol)
in methanol (25 cm3) was boiled under reflux for 10 min, then
concentrated to ca. 5 cm3 in vacuo. The precipitate was filtered
off as [CuBr2(tpm)]ؒ0.5H2O 4 (0.36 g, 83%). IR: 3347w and
3285w (NH2), 1586m (py ring), 1163m, 1118m, 1017m, 936m,
851m, 772m, 760m, 746m, 650m and 635w cmϪ1. UV–VIS
(MeOH): 709 (133) and 261 nm (ε 17600 MϪ1 cmϪ1).
Slow evaporation of a methanol solution of complex 4 in
an open tube gave crystals of [Cu2Br3(tpm)2]Brؒ3H2O 5, which
were used for X-ray crystallography. IR: 3285w (NH2), 3171w,
1591m (py ring), 1290w, 1163m, 1018m, 773m, 756m, 654m,
638w and 507w cmϪ1. UV–VIS (acetone): 713 (254) and 464 nm
(ε 707 MϪ1 cmϪ1).
A similar reaction with tpmbH rather than tpmsH gave, by
direct precipitation, [Cu(tpmb)2]ؒ3H2O 11 (79% yield). IR:
3603m, 3479m, 1647s (amide I), 1597m (py ring), 1541m,
1298m, 1244m, 1184m, 1086w, 1020m, 799w, 766m, 615m and
559m cmϪ1
.
[Cu(SO4)(tpml)(H2O)]ؒ0.5H2O 13. A solution of CuSO4ؒ
5H2O (0.11 g, 0.44 mmol) in the minimum of water was added
to a solution of tpml (0.20 g, 0.45 mmol) in ethanol (10 cm3).
The mixture was evaporated to dryness under a nitrogen
stream, then the residue was dissolved in a little ethanol. The
solution was filtered and hexane added to the filtrate, which was
kept at Ϫ10 ЊC overnight. The precipitate was filtered off and
dried in vacuo as [Cu(SO4)(tpml)(H2O)]ؒ0.5H2O 13 (0.15 g,
53%). IR: 3572m, 3246m, 3202m, 1693m (amide I), 1599m
(py ring), 1528m (amide II), 1244w, 1175s, 1113s (SO4), 1034s,
982m, 889w, 754m, 611m and 426w cmϪ1. UV–VIS (MeCN):
617 (90) and 269 nm (ε 15400 MϪ1 cmϪ1).
[Cu(tpm)2][BF4]2ؒMe2CO 6, [Cu(tpm)3][BF4]2 7, [Cu(tpma)2]-
[BF4]2 9 and [Cu(tpml)2][BF4]2 12. A solution of tpm (0.30 g, 1.1
mmol) and Cu(BF4)2ؒxH2O (0.13 g, ca. 0.43 mmol) in ethanol
(30 cm3) was stirred for 5 h. The precipitate was filtered off,
washed with ethanol, and dried in vacuo as [Cu(tpm)3][BF4]2 7
(0.32 g, 82%). IR: 3335w, 3279w and 3225w (all NH2), 1587m,
1574m and 1558m (all py ring), 1173m, 1047 (s, BF4), 995m,
789m, 777s, 751s and 519m cmϪ1. UV–VIS (MeCN): 606 (80)
and 259 nm (ε 34700 MϪ1 cmϪ1).
Addition of acetone to the green complex 7 resulted in
momentary dissolution, followed by rapid precipitation of a
blue product, which was filtered off, washed with acetone and
dried in vacuo as [Cu(tpm)2][BF4]2ؒMe2CO 6 (ca. 76%). IR:
3302m and 3248m (NH2), 1705m (acetone), 1591m and 1572w
(py ring), 1310m, 1165m, 1061s (BF4), 802w, 768m, 189m,
754m, 671m and 590m cmϪ1. UV–VIS (MeCN): 612 (111) and
260 nm (ε 24900 MϪ1 cmϪ1). Slow evaporation of an acetone
solution of 6 in an open tube gave crystals suitable for X-ray
diffraction.
The experiment was repeated with tpma instead of tpm to
give [Cu(tpma)2][BF4]2 9 (74%). IR: 3394m (NH), 1695s
(amide I), 1597m (py ring), 1267m, 1074s (BF4), 775m, 752m,
673m, 556m, 442m and 426m cmϪ1. UV–VIS (MeCN): 573 (28)
and 262 nm (ε 23900 MϪ1 cmϪ1). Diffusion of diethyl ether into
a solution of 9 in acetonitrile gave X-ray quality crystals.
Repetition of the experiment with tpml rather than tpm
gave, after evaporation to dryness, extraction of the residue
with dichloromethane and precipitation with ether, [Cu(tpml)2]-
[BF4]2 12 (72%). IR: 3383m (NH), 1682s (amide I), 1597m and
1576m (py ring), 1290w, 1215w, 1082s (BF4), 1005w, 770s,
667m, 625m, 521w and 444w cmϪ1. UV–VIS (MeCN): 583 nm
(ε 32 MϪ1 cmϪ1).
[Cu3(OAc)4(mops)2(H2O)2]ؒCH2Cl2 14. A solution of [Cu2-
(OAc)4(H2O)2] (0.13 g, 0.33 mmol) and mopsH (0.28 g, 0.71
mmol) in hot ethanol (30 cm3) was stirred for 10 min, then
filtered. The filtrate was concentrated in vacuo and ether added;
the solid was filtered off and dried in vacuo. The crude product
was dissolved in dichloromethane; addition of ether followed
by filtration gave a solid which was dried in vacuo as [Cu3-
(OAc)4(mops)2(H2O)2]ؒCH2Cl2 14 (0.17 g, 58%). IR: ca. 3337m,
br (H2O), 1686m (amide I), 1599s and 1572s (CO2 ϩ py ring),
1304m, 1267m, 1159m, 1028m, 768m and 675 cmϪ1. UV–VIS
(MeCN ϩ 10% water): 620 (79) and 268 nm (ε 18600 MϪ1
cmϪ1).
[Cu(OAc)(bops)]ؒ0.5CH2Cl2 15. A solution of [Cu2(OAc)4-
(H2O)2] (0.080 g, 0.20 mmol) in a little water was added to a
solution of bopsH (0.23 g, 0.54 mmol) in 1:1 ethanol–water
(20 cm3). The mixture was stirred for 2 min, then filtered.
The filtrate was stirred for 2 h, then concentrated to dryness
in vacuo. The residue was stirred with dichloromethane; the
resulting solution was filtered and diluted with ether, giving a
precipitate which was filtered off, washed with ether and dried
in vacuo as [Co(OAc)(bops)]ؒ0.5CH2Cl2 15 (0.033 g, 14%). IR:
3344w (NH), 1680m (amide I), 1574s, br (CO2 ϩ py ring),
1308m, 1265m, 1155w, 1028m, 989w, 799m and 768m cmϪ1
.
[Cu(OAc)2(tpm)]ؒ0.5CH2Cl2 8. A solution of [Cu2(OAc)4-
(H2O)2] (0.22 g, 0.55 mmol) in warm ethanol (10 cm3) was
added to a solution of tpm (0.30 g, 1.14 mmol) in ethanol
(10 cm3), and allowed to evaporate to dryness overnight. The
residue was dissolved in acetone, filtered, and ether added to
the filtrate. The resulting precipitate was recrystallised from
CH2Cl2–ether and dried in vacuo as [Cu(OAc)2(tpm)]ؒ0.5CH2-
Cl2 8 (0.43 g, 84%). IR: 3412m, 3273m, 1587s and 1574s
(CO2 ϩ py ring), 1335m, 1159w, 1028m, 995w, 781m, 721w,
671m and 619w cmϪ1. UV–VIS (MeOH): 615 (102) and 262 nm
(ε 17000 MϪ1 cmϪ1).
UV–VIS (MeOH): 673 (148) and 280 nm (ε 19500 MϪ1 cmϪ1).
[Cu(OAc)(tpms)(H2O)] 16. A solution of [Cu2(OAc)4(H2O)2]
(0.11 g, 0.28 mmol) and tpmsH (0.21 g, 0.57 mmol) in ethanol
(20 cm3) was stirred for 10 min, then filtered and concentrated
under a nitrogen stream. Ether was added and the mixture
stirred for 30 min, then filtered. The residue was dissolved in
boiling acetonitrile; the solution was filtered, concentrated and
diluted with ether. The precipitate was filtered off, washed with
ether and dried in vacuo as [Cu(OAc)(tpms)(H2O)] 16 (0.12 g,
45%). IR: 3390m, br (H2O), 1684m (amide I), 1595s (CO2 ϩ py
ring), 1300m, 1163m, 1024m, 758m and 664m cmϪ1. UV–VIS
(DMF): 658 (98) and 336sh nm (ε 1310 MϪ1 cmϪ1).
[Cu(tpms)2]ؒ4H2O 10 and [Cu(tpmb)2]ؒ3H2O 11. A solution
744
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[Cu4(SO4)4(bop)3] 17. A solution of CuSO4ؒ5H2O (0.15 g, 0.60
mmol) in water (5 cm3) was added to a solution of bop (0.20 g,
0.62 mmol) in methanol (10 cm3), and the solvent allowed to
evaporate to dryness overnight. The residue was triturated with
acetone, then filtered off, dried, and dissolved in acetonitrile.
The solution was filtered and diluted with ether to give a
precipitate, which was filtered off, washed with ether and dried
in vacuo as [Cu4(SO4)4(bop)3] 17 (0.055 g, 23%). IR: 3215m,
3080m, 1603s and 1574s (py ring), 1325m, 1271s, 1117s (SO4),
1028s, 988m, 802m, 772m, 721w, 656w and 604m cmϪ1
.
UV–VIS (MeOH): 664 (79), 358sh (1650) and 263 nm (ε 15000
M
Ϫ1 cmϪ1).
[{Cu(SO4)(mde)}2]ؒ3H2O 18 and [Cu(SO4)(mde)(H2O)]ؒ
0.5H2O 19. A solution of CuSO4ؒ5H2O (1.00 g, 4.0 mmol) in
water (10 cm3) was added to a stirred solution of mde (0.994 g,
4.1 mmol) in methanol (40 cm3). The mixture was stirred for
5 h, then concentrated in vacuo, to give an oil. This was stirred
with acetone and the resulting solid filtered off, dried, and
extracted with methanol. Filtration gave a turquoise solid
A plus a dark green filtrate B. Solid A was dissolved in wet
methanol, and acetone was added to the filtrate until the first
permanent precipitate. The mixture was kept at Ϫ10 ЊC over-
night, then decanted and the decantate concentrated to dryness
in vacuo. The residue was recrystallised from wet methanol–
acetone as above as [{Cu(SO4)(mde)}2]ؒ3H2O 18 (0.42 g, 25%).
IR: 3370w and 3205w (NH), 1593m and 1570w (py ring),
1165m, 1086s (SO4), 1026m, 764w, 721w and 606m cmϪ1
.
UV–VIS (water): 657 nm (ε 36 MϪ1 cmϪ1). X-Ray quality
crystals were obtained overnight by diluting a solution of
complex 18 in methanol–water with acetone.
Filtrate B was concentrated to dryness in vacuo, and the
residue dissolved in the minimum of methanol. The solution
was filtered and excess of ether was added to the filtrate.
The precipitate was filtered off, washed with ether and dried
in vacuo as [Cu(SO4)(mde)(H2O)]ؒ0.5H2O 19 (0.70 g, 40%).
IR: 3396w and 3217w (NH), 1605m and 1572w (py ring),
1117s (SO4), 1032m, 972m, 777m, 721w and 613m cmϪ1
.
UV–VIS (MeOH): 671 (83), 360 (2310) and 261 nm (ε 11200
M
Ϫ1 cmϪ1).
[Zn(tpm)(H2O)3]2[Zn(H2O)6][SO4]3ؒ3H2O 20. tpm (1.11 g,
6.0 mmol) was dissolved in methanol (100 cm3). To the warm
solution was added dropwise a solution of ZnSO4ؒ7H2O (1.73
g, 6.0 mmol) in water (20 cm3). The solution was heated gently
for 30 min, then filtered whilst still hot and allowed to cool in an
open beaker. The white precipitate was collected by filtration,
washed with two 5 cm3 portions of ethanol, followed by 5 cm3
of diethyl ether, and air-dried as [Zn(tpm)(H2O)3]2[Zn(H2O)6]-
[SO4]3ؒ3H2O 20 (1.62 g, 63%) (Found: C, 30.3; H, 4.6; N, 8.8.
Calc. for C32H52N8O24S3Zn3ؒ3H2O: C, 30.0; H, 4.6; N, 8.8%).
UV–VIS (water): 269 (34800) and 262 nm (ε 38400 MϪ1 cmϪ1).
ΛM(water): 501 S cm2 molϪ1. IR: 3385m (br, H2O), 3265w,
1595m (py ring), 1464m, 1441m, 1109s, br (SO42Ϫ), 1020m,
773m, 758m, 656m, 640m and 617m cmϪ1. Several crops having
identical IR spectra were obtained. Crystals suitable for X-ray
crystallography were grown by slow diffusion of 2-propanol
into a saturated aqueous solution.
[Cu(tpm)(NCMe)]PF6ؒ0.33Et2O 21. Dry acetonitrile (20
cm3) was added to a solid mixture of tpm (0.2 g, 0.76 mmol)
and [Cu(NCMe)4]PF6 (0.28 g, 0.76 mmol), and the resulting
solution was stirred for 5 h, then concentrated in vacuo to ca. 5
cm3. Addition of ether gave a precipitate, which was isolated by
Schlenk filtration. The crude product was recrystallised from
acetonitrile–ether as [Cu(tpm)(NCMe)]PF6ؒ0.33Et2O 21 (0.33
g, 81%). 1H NMR (CD3CN): δ 8.57 (br m, 3H, H6), 7.85 (br m,
3H, H4), 7.41 (br m, 3H, H3), 7.13 (br m, 3H, H5), 4.20 (br, 2H,
NH2) and 1.95 (s, 3H, CH3CN); spectrum also shows ether in
the correct ratio. 13C-{1H} NMR (CD3CN): δ 161.3 (C2), 150.1
J. Chem. Soc., Dalton Trans., 2001, 736–746
745

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(C6), 138.4 (C4), 124.5 (C3) and 70.9 (CNH2). 31P NMR
(CD3CN): δ Ϫ285.5 (s, JPF = 706 Hz, PF6Ϫ). IR: 3389w and
3330w (NH2), 1587m (py ring), 1149m, 1114m, 1013m, 962m,
901m, 838s (PF6), 770m, 752m, 651m, 635m, 555m, 489w and
Acknowledgements
We thank the BBSRC for financial support for this work, and
EPSRC for a ROPA award (to P. C. S.). Dr M. Cocksedge is
thanked for help with mass spectra.
418m cmϪ1
.
Crystal structure analyses
References
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19 D. F. Shriver, Inorg. Synth., 1979, 19, 90.
The crystal structure analysis of [Cu(SO4)(tpm)(H2O)]ؒ3H2O 1
is described here. The other compounds were examined by very
similar procedures. Crystallographic and refinement data for all
the complexes are collated in Table 3, and further crystallo-
graphic features are included below; all intensity data were
measured at 293 K.
Crystals of complex 1 were thick, turquoise plates. One,
mounted on a glass fibre, was examined photographically,
then transferred to an Enraf-Nonius CAD4 diffractometer
(with monochromated radiation) for determination of accurate
cell parameters and for measurement of diffraction intensities.
During processing, corrections were applied for Lorentz-
polarisation effects, absorption (by semi-empirical ψ-scan
methods) and to eliminate negative net intensities (by Bayesian
statistical methods). No deterioration correction was necessary.
The structure was determined by the direct methods routines
in the SHELXS program20 and refined by full-matrix least-
squares methods on F 2 in SHELXL.21 Hydrogen atoms on
the pyridyl rings were included in idealised positions; the two
amino hydrogens were located in a difference map and refined
with geometrical constraints. The isotropic thermal param-
eters of all hydrogen atoms were allowed to refine freely. The
sulfate ligand is disordered in two orientations, sharing a
common site for the coordinated oxygen atom. Four water
molecules were identified, one bound to the copper atom, and
three as free solvent molecules; two of these last are dis-
ordered over pairs of sites with the same ratio of major:
minor occupancies (0.65:0.35) as for the sulfate ligand. The
non-hydrogen atoms (except for the minor components of the
solvent oxygens) were refined with anisotropic thermal
parameters.
Scattering factors for neutral atoms were taken from refer-
ence 22. Computer programs used in this analysis have been
noted above or in Table 4 of reference 23, and were run on a
DEC-AlphaStation 200 4/100 in the Department of Biological
Chemistry, John Innes Centre.
Crystals of [Zn(tpm)(H2O)3]2[Zn(H2O)6][SO4]3ؒ3H2O, 20,
were twinned, with one twin’s diffraction pattern superimposed
precisely on that of the second twin. Data for the composite
crystal were recorded and, using the TWIN/BASF routines in
SHELXL, the structure of each twin was determined and
refined well; the refinement of BASF showed that the ratio of
twins was ca. 62:38.
20 G. M. Sheldrick, Acta Crystallogr., Sect. A, 1990, 46, 467.
21 G. M. Sheldrick, SHELXL, Program for Crystal Structure
Refinement, University of Göttingen, 1993.
22 International Tables for X-Ray Crystallography, Kluwer Academic
Publishers, Dordrecht, 1992, vol. C, pp. 193, 219 and 500.
23 S. N. Anderson, R. L. Richards and D. L. Hughes, J. Chem. Soc.,
Dalton Trans., 1986, 245.
CCDC reference number 186/2326.
See http://www.rsc.org/suppdata/dt/b0/b008476j/ for crystal-
lographic files in .cif format.
24 W. J. Geary, Coord. Chem. Rev., 1971, 7, 81.
746
J. Chem. Soc., Dalton Trans., 2001, 736–746